Inflammation is defined as the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. It is a protective attempt by the organism to remove the injurious stimuli as well as initiate the healing process for the tissue. Inflammation may be acute (early phase of response) or chronic (occurs over a long time). Acute inflammation involves polymorphonuclear neutrophil leukocytes while chronic inflammation involves monocytes, macrophages, lymphocytes and plasma cells (collectively, mononuclear leukocytes). One affect of both acute and chronic inflammation is the sensation of pain which can be either neuropathic or nociceptive. Some common ailments associated with neuropathic pain are lower back pain, neuralgia/fibromyalgia, diabetic neuropathic pain and pain associated with multiple sclerosis. Common ailments associated with nociceptive pain are arthritic pain, particularly osteoarthritis and rheumatoid arthritis, post-operative pain, cancer-related pain and HIV-related pain.
In 1997 the research group of Sommer and coworkers (Sommer C, Schmidt C, George A, Toyka K V. Neurosci Lett. 1997; 237: 45-48) showed that epineural injection of a potent matrix metalloproteinase inhibitor (TAPI-0) in the chronic constriction injury (CCI)-mouse model was able to block both mechanical allodynia and thermal hyperalgesia after the third day of daily injections. At the time the authors concluded that inhibition of TNF-alpha was the mechanism of action since the inhibitor (TAPI-0) was a known inhibitor of TNF-alpha (IC50˜100 nM). However, subsequently it has been shown that TABI-0 has a IC50 for MMP-9 of 0.5 nM.
Ji and coworkers (Nature Medicine 14 (13), (2008), 331-336) have recently found that matrix metalloproteinase-9 (MMP-9) was upregulated in injured dorsal root ganglion (DRG) primary sensory neurons in the early phase of the L5 spinal nerve ligation (SNL) neurophathic pain model (first day and then declining after 3rd day) and that matrix metalloproteinase-2 (MMP-2) had a delayed response in the model (upregulation starting from day 7 and still present on day 21). They also found that MMP-2 induces neuropathic pain by IL-1β cleavage and astocytic extracellular signal-regulated kinase (ERK) activation. They also found that endogenous matrix metalloproteinase inhibitors (TIMP-1 and TIMP-2) also suppressed neuropathic pain in the model. Kobayashi and coworkers (Molecular and Cellular Neuroscience, 39, (2008), 619-627) recently demonstrated that MMPs degrade peripheral myelin basic protein (MBP) and that a broad spectrum, hydroxamic acid containing MMP inhibitor (GM6001) was found to attenuate mechanical nociception. There have been other studies by other groups using knock out mice (Komori K., et al. FEBS Lett., 557: 125-128, (2004) and Folguera, A.; et. al PNAS, 106(38), 16451-16456 (2009)) demonstrating that MMP-2 is critical for inducing chronic neuropathic pain.
Among chronic users of opioids both tolerance and hyperalgesia frequently occur. Tolerance is a state of adaptation in which exposure to the opioid induces changes that result in a lowering of the drug's pain blocking effects over time. The result of tolerance is that the user requires higher dosages of the opioid to maintain a therapeutic effect. Hyperalgesia is a state in which exposure to the opioid sensitizes the user to pain. Patients who chronically use opioids such as morphine become not only sensitize to the original pain but in many cases report new types of pain while on the opioid itself. Both tolerance and hyperalgesia are factors that help explain opioids prevalence for addiction among chronic users. Recently, Song and coworkers (The Journal of Neuroscience, 30(22), (2010), 7613-7623) found a strong link between the physical dependence due to opioid withdrawal and enhanced MMP-9 activity in the dorsal horn. These researchers found that by administering exogenous MMP-9 in the spine they could induce both morphine-like withdrawal behavior as well as mechanical allodynia in normal mice. When the researchers injected intrathecally a MMP-9 inhibitor (2-[Benzyl-(4-methoxy-benzenesulfonyl)-amino]-5-diethylamino-N-hydroxy-3-methyl-benzamide) in mice undergoing morphine withdrawal they could eliminate the withdrawal behaviors. When they co-administered either a MMP-2 or a MMP-9 inhibitor they could significantly reduce morphine tolerance in mice. The compounds that had been used in all of the above studies to block either MMP-2 and/or MMP-9 activity were hydroxamic acid containing MMP inhibitors that have known toxic side-effects.
Matrix metalloproteinases (MMPs) are a family of structurally related zinc-containing enzymes that have been reported to mediate the breakdown of connective tissue in normal physiological processes such as embryonic development, reproduction, and tissue remodelling. Over-expression of MMPs or an imbalance between MMPs has been suggested as factors in inflammatory, malignant and degenerative disease processes characterized by the breakdown of extracellular matrix or connective tissues. MMPs are, therefore, targets for therapeutic inhibitors in several inflammatory, malignant and degenerative diseases such as rheumatoid arthritis, osteoarthritis, osteoporosis, periodontitis, multiple sclerosis, gingivitis, corneal epidermal and gastric ulceration, atherosclerosis, neointimal proliferation (which leads to restenosis and ischemic heart failure) and tumor metastasis but not pain. MMP-2 (72 kDa gelatinase/GelatinaseA) and MMP-9 (92 kDa gelatinase/GelatinaseB) degrade the extracelluar matrix components of the basement membrane. Their substrates include types IV and V collagen, fibronectin, elastin, and denatured interstitial collagens. Matrix degradation attributed to this proteinase has been shown to play an important role in the progression of such diseases as atheroslerosis, inflammation, stroke, and tumor growth and metastasis. However until recently, there has not been very much scientific literature published on the use of MMP-2 and/or MMP-9 inhibitors to treat pain and/or addiction.
Matrix metalloproteinase have been tested clinically in a few indications. Most predominantly in arthritis and cancer. Inhibitors that have entered clinical trials specifically for an oncologic indication include prinomastat (AG3340; Agouron/Pfizer), BAY 12-9566 (Bayer Corp.), batimistat (BB-94; British Biotech, Ltd,), BMS-275291 (formerly D2163; Celltech/Bristol-Myers Squibb), marimastat (BB 2516; British Biotech, Ltd./Schering-Plough), MMI270(B) (formerly CGS-27023A; Novartis), and Metastat (COL-3; CollaGenex). Many of the hydroxamic acid containing inhibitors exhibit very broad toxicities in humans. For example, Marimastat, which contains a hydroxamate moiety, exhibited time-dependent and dose-dependent musculoskeletal toxicities (arthralgia, myalgia, tendinitis) in humans. Other toxicities for marimastat include ascites, disseminated carcinoma, chills, cholangitis, dizziness, dyspnea, edema, fatigue, fever, gastrointestinal (anorexia, nausea, vomiting, diarrhea, constipation), gastrointestinal hemorrhage, headache, heartburn, hepatic toxicity, hypercalcemia, hyperglycemia, rash, and shortness of breath. It is not known whether the toxicities exhibited by many of the MMP inhibitors are attributed to the hydroxamic acid moiety contained in many of these broad spectrum MMP inhibitors, however, it is clear that having an MMP inhibitor that does not contain a hydroxamic acid group could reduce some of the potential metabolic liabilities.
Kushner and coworkers (Kushner, D. J.; Baker, A.; Dunstall, T. G. Can J. Physiol Pharmacol, 77(2), (1999) p. 79-88) have presented examples of how incorporating deuterium into a drug can often reduce the level of metabolic induced transformations especially those mediated by Cytochrome P450. This reduce rate of Cytochrome P450 induce metabolism can sometimes translate directly to enhanced bioavailability. The reason for this is due to the fact that atomic substitution of a hydrogen by a deuterium in a drug alters the strength of the carbon-deuterium bond of the drug, while keeping it's 3D surface very similar to that of the nondeuterated version. Substitution of deuterium for hydrogen, can give rise to an isotope effect that can alter the pharmacokinetics of the drug. In a reaction in which the cleavage of a C—H bond is rate determining the same reaction of the C-D analogue will be reduced. For example Schneider and coworkers (Scheneider, F.; et al., BiRDS Pharma GmbH, Arzneimittel Forschung (2006), 56(4), p. 295-300) have shown that replacing several of the hydrogen atoms around one of the aromatic rings of the COX-2 inhibitor Refecoxib (4-(4-methylsulfonylphenyl)-3-phenyl-5H-furan-2-one) with deuterium (at positions 2′,3′, 4′,5′ an 6′) enhanced the oral bioavailability of the drug without affecting it's COX-2 selectivity. If one applied this strategy to the tryptophan based acid S-3304 one could reduce its susceptibility to cytochrome P-450 hdyroxylation and ultimately enhance its overall bioavailability and possibly it's target tissue compound concentration.
Another possible affect of incorporating deuterium into a drug is on its polymorphic (i.e., different crystalline forms) properties. For example, Hirota and Urushibara (Bulletin of the Chemical Society of Japan, 32(7), (1959), 703-706) have shown that replacing a single vinylic hydrogen for deuterium on Allocinnamic acid can change both the melting point and the intensity of the x-ray diffraction pattern of the molecule. Lin and Guillory (Journal of Pharmaceutical Science, Vol. 59(7), (2006), 972-979) have shown that sulfanilamide-d4 exhibited smaller heats of transition and heats of fusion for its various crystalline states as compared to it's corresponding non-deuterated forms. Finally, Crawford and co-workers (Crawford, S. et al., Angewandte Chemie International Edition, 48(4), (2009), 755-757) recently showed that the crystalline form of fully deuterated pyridine adopts a unique configuration that can only be obtained under high pressure with the non-deuterated parent. Their work clearly showed that replacing hydrogen for deuterium changes the strength of interaction between various atoms in neighboring molecules causing a change in the crystalline arrangement to one that is more energetically favorable. This change in crystalline arrangement or polymorph may allow for improved dissolution properties and enhanced bioavailability.
Sucholeiki (WO/2010/075287) has shown that partially deuterating a matrix metalloproteinase (MMP) inhibitor can enhance the bioavailability of that inhibitor as compared it's non-deuterated parent. In human blood, the MMP inhibitor S3304 was known to form several hydroxylated metabolites (Chiapppori, A. A. et al. Clin. Cancer Res. 2007, 13(7), 2091-2099). Two of the main metabolites involved hydroxylation around the indole ring of the tryptophan moiety and a third involved hydroxylation of the toluene methyl portion of the S3304 molecule. When the terminal toluene methyl portion of S3304 was deuterated, the compound was observed to exhibit greater in-vivo biological activity in the spinal nerve ligation (SNL) mouse model for mechanical allodynia as compared to vehicle control and non-deuterated parent (S3304).
There are a few non-hydroxamic acid containing MMP inhibitors that have appeared in the literature, a much smaller set of these have been tested clinically in cancer and/or inflammation. None of these, however, have been tested against pain or to reduce the tolerance and withdrawal associated with opioid use in animal models or humans. A series of MMP-2 and/or MMP-9 inhibiting compounds is presented and a method for their use in inhibiting pain and other diseases is disclosed.